In accordance with point (1), a boundary condition affecting the enthalpy of the material in one of the cells in a grid will be expressed as an additional thermal-energy source in the cell; and there may be many sources for a single cell, each representing a different physical effect or boundary condition. Thus, if there are several contributors to the source, the total contribution is given by,
Addition of the foregoing source to the numerator of the right-hand side of equation (2.4-6), followed by re-arrangement, leads to the following equation for jP: